The present invention is directed to a surgical tool employed to cut a circular opening of a specific diameter through the skin of a patient in connection with the implanting of a percutaneous access device.
Percutaneous access devices, hereinafter PAD, are employed to provide a through-the-skin connection between an external device and some instrument or other device implanted within a patient's body. PAD's are employed on a long-term or permanent basis as, for example, to provide external pneumatic and electrical connections to an implanted left ventricle assist device or dynamic aortic patch of the type disclosed in U.S. Pat. No. 4,630,597. A PAD of the general type with which the present invention is concerned is disclosed in U.S. Pat. No. 4,634,422 and consists basically of a body having a circular flange which is implanted beneath the patient's skin and a projection which projects coaxially from one side of the flange outwardly through the patient's skin. Electrical or pneumatic leads from within the patient's body are led through a passage through the projection of the PAD to a point where they are accessible from the exterior of the patient's body.
As set forth in greater detail in U.S. Pat. No. 4,634,422, in order to implant the PAD, at some stage during the implantation procedure it is necessary to cut a circular opening through the patient's skin to provide a passage for the projection to which the connections to external devices will be made. The outer layer of skin--i.e. the epidermis--has a natural propensity to attempt to close this surgical opening, and in U.S. Pat. No. 4,634,422 there is described in detail a technique for firmly bonding the underlying dermal layer of skin to the sidewall of the projection to prevent the down growth of epidermis around the implanted device.
The formation of a bond between the dermal layer of skin and the projection of the PAD is a delicate and time-consuming operation which, as might be expected, requires a precise and uniform initial "fit" between the edge of the circular opening cut through the dermis and the outer periphery of the projection of the PAD. The diameter of the opening through the dermis may be closely matched to the outer diameter of the projection by selection of the appropriate size of the trephine employed to cut the opening through the skin. However, due to the resilience of the skin, the trephine does not cut an opening with truly cylindrical sidewalls, but instead produces an opening of a frusto-conical configuration with the large diameter end of the opening facing outwardly of the skin. In that the outer sidewall of the PAD projection typically is cylindrical or tapered upwardly with an opposite inclination to that of the opposed sidewall of the opening cut through the skin, the "fit" between the projection of the PAD and the upper or outermost portion of the dermal layer is loose where it has the greatest need to be tight, greatly increasing the possibility of delayed or inadequate bonding between the dermal layer and projection, as well as increasing the risk of development of infection.
The present invention provides a surgical tool operable to cut a circular opening through the skin of a patient whose diameter increases with depth from the exterior surface of the skin.